Angle indicator for capsular bag size measurement

ABSTRACT

Implantation of an accommodating intraocular lens in an eye may require the accurate measurement of the size, circumference, or diameter of the capsular bag of the eye. After the natural crystalline lens has been surgically removed, a flexible ring may be temporarily or permanently inserted into the capsular bag for measuring the circumference of the capsular bag. The ring is generally compressible to fit through a surgical incision, then expands to fill the capsular bag along an equatorial region. The ring has a central component that changes shape as the ring is compressed. The shape change is generally correlated to the size of the capsular bag and may be measured visually or with a camera through the cornea, the measurement being generally independent of corneal magnification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method and apparatus formeasuring the size of the capsular bag of a human eye.

2. Description of the Related Art

Recently, a great deal of effort has been devoted to developing anaccommodating intraocular lens, which can adjust its power over aparticular range to clearly view both near and far objects. Theaccommodating intraocular lens is generally inserted into the capsularbag of the eye, which is a transparent structure that houses the naturallens of the eye and generally remains in the eye after the natural lenshas been surgically removed.

The accommodating intraocular lens changes its power in response to asqueezing and/or expanding force applied to the lens by the capsular bagvia the ciliary muscle.

It is generally important to know the size (or more precisely, the innerdiameter or circumference) of the capsular bag for each patient's eye,prior to insertion of the intraocular lens. The capsular bag size mayvary patient-to-patient or eye-to-eye, and if the bag is larger orsmaller than expected, the lens may end up slightly expanded or squeezedupon implantation. This, in turn, may result in a shift in the nominalbase power and/or a reduction in the accommodation range, both of whichare undesirable.

Although the capsular bag diameter is a desirable and useful quantity,it is also quite difficult to measure.

There have been attempts to measure the capsular bag size withultrasound. While ultrasound may be useful for determining the centralthickness of the unoperated lens, it is not generally versatile enoughto image the entire crystalline lens, and cannot reliably read out tothe perimeter of the lens.

There have been attempts to measure the capsular bag by inserting acapsular tension ring (CTR) into the eye. See, for instance, K. STRENN,R. MENAPACE, and C. VASS, “Capsular bag shrinkage after implantation ofan open-loop silicone lens and a poly(methyl methacrylate) capsuletension ring,” J Cataract Refract Surg, 1997, pp. 1543-1547, Vol. 23,which is hereby incorporated by reference in its entirety. In thisreference, a CTR indicates the capsular diameter, based on linearmeasurement of a peripheral gap. After the measurement, the CTR isgenerally not removed from the eye and remains resident in the eye,which may be undesirable.

There have been attempts to correlate capsular bag size with other eyeproperties that can be measured more easily. See, for instance, C. VASS,R. MENAPACE, K. SCHMETTERER, O. FINDL, G. RAINER AND I. STEINECK,“Prediction of pseudophakic capsular bag diameter based on biometricvariables,” J Cataract Refract Surg, October 1999, pp. 1376-1381, Vol.25, which is hereby incorporated by reference in its entirety. In thisreference, measurements of capsular bag diameter were taken on a sampleof patients, using the CTR noted above. In addition, measurements ofcorneal power and axial length were taken on the same patients, usingknown methods. A regression analysis of the measurements produced astatistically significant correlation between capsular bag diameter andcorneal power and axial length, but not with a sufficient accuracy forpredicting the required size of an accommodating intraocular lens.

There have been attempts to convert the capsular bag circumferencedimension to a linear dimension, then to measure the linear dimensionwith a camera or visually. See, for instance, M. TEHRANI, H. B. DICK, F.KRUMMENAUER, G. PFIRRMANN, T. BOYLE and B. STOFFELNS, “Capsule measuringring to predict capsular bag diameter and follow its course afterfoldable intraocular lens implantation,” J Cataract Refract Surg,November 2003, pp. 2127-2134, Vol. 29, which is hereby incorporated byreference in its entirety. In this reference, a Koch capsule measuringring is inserted into the eye. The ring is an incomplete circle, withappendices on each end, so that when the ring is inserted into thecapsular bag, the separation between the appendices is related to thecapsular bag circumference. The ring is left in the eye after themeasurement is taken, which may be undesirable.

In addition, for the above reference, the measurement of the appendixseparation may be disadvantageous for two reasons. First, themeasurement is taken at the peripheral edge of the eye, which is adifficult region of the eye for measurement. For instance, the region tobe measured might be outside the area of the pupil, and might requireuse of a slitlamp, or unusual and undesirable handling of the pupil.Second, it is difficult to measure a linear dimension in the eye. Often,such a measurement is taken through the cornea, which can magnify thelinear dimension, especially at the periphery of the eye. Becausecorneal powers may vary from patient-to-patient and eye-to-eye, theremay be a significant uncertainty in any linear measurements takenthrough the cornea. In addition, because most eye surgery is performedthrough a microscope, the measurement may have to be taken through themicroscope, which may have a zoom feature or a variable focal lengththat may further complicate a linear dimension measurement.

Accordingly, there exists a need for an apparatus and method formeasuring the size of the capsular bag of an eye, which does not rely ona linear measurement at the periphery of the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method of replacing a lens in the capsularbag of an eye.

FIG. 2 is a schematic drawing of an angle indicator at three exemplarycapsular bag sizes.

FIG. 3 is a front-view plan drawing of the angle indicator of FIG. 2.

FIG. 4 is a schematic drawing of an approximate geometry of the angleindicator of FIGS. 2 and 3.

FIG. 5 is a plot of capsular bag diameter versus measured angle a, for avariety of straight segment lengths, for the approximate geometry ofFIG. 4.

FIG. 6 is a close-up of the q=0.6 plot of FIG. 5.

FIG. 7 is an isometric drawing of a protractor.

FIG. 8 is a plan drawing of the protractor of FIG. 7.

DETAILED DESCRIPTION OF THE DRAWINGS

Implantation of an accommodating intraocular lens in an eye may requirethe accurate measurement of the circumference, or, equivalently, thediameter of the capsular bag of the eye. After the natural crystallinelens has been surgically removed, a flexible ring may be temporarilyinserted into the capsular bag for measuring the circumference of thecapsular bag. The ring compresses to fit through a surgical incision,then expands to fill the capsular bag along an equatorial region. Thering has a central component that changes shape as the ring iscompressed, where a relatively small change in circumference produces arelatively large change in shape. The shape may be measured visually orwith a camera through the cornea, and is independent of corneal orcamera magnification. The ring extends into the center of the capsularbag and is compliant, so that it may be safely removed by grasping thecentral features and withdrawing it from the capsular bag.

FIG. 1 is a flow chart of an exemplary method 10 of replacing a lens inthe capsular bag of an eye.

In element 11, the lens is removed from the capsular bag of the eye. Theremoved lens may be the natural crystalline lens of the eye, which hasbecome opaque due to cataracts, or has become damaged by some otherdisease or injury. Alternatively, the removed lens may be an existingintraocular lens. Typically, the lens is removed in a surgical procedurein which the lens is broken up and vacuumed out of the eye. The capsularbag, which supports the lens before removal, is retained in the eye, andmay be used to support a replacement lens.

The replacement lens may be an accommodating intraocular lens, whichrelies on forces transferred by the zonular fibers in the eye to thecapsular bag. These forces can change the power and/or location of thelens by distorting and/or translating one or both of the lens surfaces.The distorting force exerted by the zonular fibers is limited by thefinite strength of the lens capsule, fibers, and surrounding structures,and typically the intraocular lenses are designed to use this limitedforce to change power to cover all or part of the range of accommodationfor the eye. As a result, the intraocular lens may be quite sensitive tocompressive or expansive forces applied to its equator, and may bedesigned to work optimally for a particular size of capsular bag. If thepatient's capsular bag is larger or smaller than expected, theintraocular lens may experience a shift in nominal power, or atruncation of the accommodation range, which may be undesirable.Accordingly, it may be useful during a surgical procedure to measure theactual size of the capsular bag, so that an intraocular lens may beselected for implantation that corresponds to the actual size of thecapsular bag.

In element 12, an angle indicator is inserted into the capsular bag.During insertion, it is often desirable to use as small an incision aspossible, so the angle indicator may optionally be inserted in a foldedstate.

In element 13, the angle indicator is expanded to coincide with adiameter of the capsular bag. If the angle indicator is inserted in afolded state, it may be first unfolded to reach its full size. Thecapsular bag material is flexible, so that it may be bent and reshaped.It may be relatively straightforward to position the angle indicator,which is generally ring-shaped, along the equator of the capsular bag.Typically, some gentle, back-and-forth motions applied by the surgeonare sufficient to move the angle indicator to lie along the equator ofthe capsular bag. In general, the shape of the empty capsular bag issuch that it may be well-approximated as circular when viewed from thefront. Any azimuthal errors in the positioning of the angle indicator donot significantly affect the angular reading from the angle indicator,or the measured value for the capsular bag size.

In element 14, once the angle indicator is aligned along the equator ofthe capsular bag, the angle is read from the angle indicator. The anglemay be formed from the intersection of two generally straight elementson the angle indicator, and may be read from a roughly central portionof the angle indicator, rather than at an edge of the angle indicator.The angle may be seen visually by the surgeon or by a camera ormicroscope trained on the eye.

In element 15, once the angle has been read, the angle indicator may beremoved from the capsular bag of the eye. The angle indicator may befolded upon itself for removal, which is especially convenient if theangle indicator is inserted in the folded state. Alternatively, theangle indicator may be broken or separated into segments, and then thesegment may be removed through the incision in the eye. In oneembodiment, the angle indicator includes cutaways on its posteriorsurface, which may allow sectioning in vivo for removal of the angleindicator.

In element 16, once element 14 has been performed and the angle is readfrom the angle indicator, the read angle is converted to a capsular bagsize. The size may be reported as a diameter, or, equivalently, as acircumference. The conversion may be done by reading values off aprinted table, by reading values off a graph, by plugging the read angleinto a predictive formula, by a computer, or directly by comparing theangle to a dedicated device.

In element 17, once element 16 has produced a value of the capsular bagsize, an intraocular lens may be selected. The lens selection may bebased in part on the capsular bag size, as well as on other data, suchas the required lens power.

For instance, for a given required nominal lens power, there may beseveral intraocular lenses available, each sized for a particularcapsular bag diameter. The available lenses may be part of a kit, withdiameter spacings of 0.5 mm, 0.25 mm, 0.2 mm, 0.15 mm, 0.1 mm, 0.05 mm,or any suitable value. Typically, the exact size value given fromelement 16 may not be exactly available in the kit, and the surgeon orpractitioner may have to round off to the nearest size that is availablein the kit.

Alternatively, the intraocular lens may have an adapter that can attachto the circumference of the lens, which allows a single lens to be usedwith multiple sizes of capsular bags.

As a further alternative, the intraocular lens may itself be adjustable,for instance, with an adjustable haptic that can couple a particularoptic to a capsular bag sized within a particular range.

In element 18, once an intraocular lens is selected from element 17, theselected lens may be surgically implanted in the capsular bag.

Note that element 15 follows element 14, and elements 16 and 17 followelement 14, but elements 16 and 17 need not follow element 15. Forinstance, element 15 may follow element 17, which follows element 16,which follows element 14. The conversion of the read angle to a capsularbag size and the selection of a lens based on the capsular bag size areessentially independent of removal of the angle indicator from thecapsular bag, and these elements may be performed in any suitable order.

A schematic drawing of the angle indicator itself is shown in FIG. 2.The angle indicator is shaped roughly like a broken ring, with thebroken portion of the ring replaced by two segments that connect nearthe center of the ring. The ring is inserted into the capsular bag andexpands until it is coincident with a diameter of the capsular bag. Asthe ring itself expands and contracts, the angle between the twosegments increases and decreases.

The ring may be designed so that a relatively small change in diameterproduces a relatively large change in angle. For instance, threeexemplary diameters D1, D2 and D3, are shown in FIG. 2, along with theircorresponding angles A1, A2 and A3. The relationship between measuredangle and ring (and, therefore, capsular bag) diameter is shown in theexemplary plot in FIG. 2. Note that the relationship need not be trulylinear, as shown in FIG. 2, but may have any suitable increasingrelationship, such as a quadratic or more complex polynomialrelationship. During use, the practitioner inserts the angle indicatorinto the capsular bag, expands the angle indicator to fill the capsularbag, reads the angular value from angle indicator, and converts the readangular value to a capsular bag diameter, or equivalently,circumference.

Note that the angle is viewable near the center of the pupil of thelens, rather than only at the edge of the pupil or the edge of thecapsular bag. This reduces the need for unusual viewing techniques, orextra handling of the pupil, and may help reduce distortion of the anglewhen viewed through the patient's cornea.

Note also that the angle indicator remains essentially round, for allangles/diameters within a particular range. This is accomplished byvarying the radial thickness of the ring, with a maximum thicknessopposite the two segments, and a minimum thickness in the regionsadjacent to the joints that attach the straight segments to the rest ofthe ring. This is shown more clearly in FIG. 3.

FIG. 3 is a front-view plan drawing of an angle indicator 30. Anincomplete annulus 31, shaped generally as an open-ended ring-shapedportion, is hingedly connected to two straight sections 32 and 33 thatare hingedly connected to each other in the interior of the circle.

The incomplete annulus 31 may optionally have a varying radial thicknessaround its circumference. Adjacent to the hinges 34 and 35, the radialthickness 36 may be its minimum. The radial thickness may increasefarther away from the hinges 34 and 35, reaching an intermediate value37 partially around the ring, and may finally reach a maximum value 38directly opposite and between the hinges 34 and 35. Alternatively, theradial thickness may be constant around its circumference, or may varyin a manner other than the exemplary manner described above.

In the exemplary design of FIG. 3, the out-of-plane thickness isessentially constant along the incomplete annulus 31 and segments 32 and33. The corners may be rounded, or may be ungrounded.

The variation in radial thickness around the ring helps ensure that theincomplete annulus stays essentially round, even as the angle betweenthe straight segments 32 and 33 varies. As such, the diameter dimensionsD1, D2 and D3 in FIG. 2 are truly diameters, and the outermost shape ofthe angle indicator is essentially round at each of the three sizesshown. The angle indicator 30 retains its round periphery as it iscompressed.

Alternatively, the radial thickness of the angle indicator 30 may remainessentially constant around the ring, and the out-of-plane thickness mayvary along the ring. As a further alternative, both the radial thicknessand the out-of-plane thickness may vary around the ring.

The hinges 34 and 35 may be formed integrally as weakened portions ofthe angle indicator 30. In one embodiment, the hinges 34 and 35 areformed at regions of reduced in-plane thickness at the intersections ofthe straight segments 32 and 33 with the incomplete annulus 31. As such,the hinges 34 and 35 may bend freely in the in-plane direction, allowingthe angle indicator to freely expand and contract to attain its maximumsize inside the capsular bag. The hinges 34 and 35 do not freely permitmovement of the two segments 32 and 33 out of the plane of the angleindicator 30.

The segments 32 and 33 are joined to each other by a third hinge 39,which is also formed as a reduction in the in-plane thickness near thehinge, also permits free in-plane movement of the segments with respectto each other and free diametric expansion and compression of the angleindicator 30, and also restricts out-of-plane movement.

Note that the segments 32 and 33 are shown in the figures as beingentirely straight. In practice, there may be some curvature to all or aportion of either or both of the segments. For instance, there may besome local waviness to all or a portion of the segments 32 and 33.Alternatively, there may be a more global curvature, having a radius onthe order of or larger than the angle indicator radius. In oneembodiment of the angle indicator, the segments 32 and 33 are straightthroughout.

Note that the angle indicator may measure capsular bags having a sizelarger than the incision through which the angle indicator is inserted.For instance, the angle indicator may measure capsular bag diameters onthe order of 11 mm, and may fit through incisions on the order of 3 mm.As such, the angle indicator may be compressed in an injector or foldedupon itself during insertion (and later, during extraction), and may beunfolded and expanded for performing the measurement.

During insertion and positioning of the angle indicator 30, it may bebeneficial to gently “force open” the straight segments 32 and 33 of theangle indicator 30. This may be accomplished by applying a force on ornear the rear (essentially flat) side of the hinge 39, directed outwardfrom the ring, toward the opening between the segments. The force may beapplied by the practitioner using the equipment that is typically usedto position objects during surgery, such as a hook or forceps. Becausethe force may be applied directly to angle indicator 30, there may be noneed for extra holes or tabs for this purpose, although holes and/ortabs may optionally be used.

The length of the segments 32 and 33 may be varied, so that the hingethat joins them may fall on either side of the center of the ring at itsnominal position. As the segment length is increased, the angle becomeseasier for the practitioner to read during use, although the sensitivityis decreased. Likewise, as the segment length is decreased, the anglebecomes more difficult for the practitioner to read during use, but thesensitivity is increased. In practice, the designer of ordinary skill inthe art understands this trade-off, and may design an angle indicator 30with a suitable range of operation, a suitable sensitivity, and asuitable ease of angle viewing.

Optionally, there may be more than one angle indicator for a particulareye, with each angle indicator covering a particular range of capsularbag sizes. For instance, one angle indicator may be used for capsularbag diameters in the range of 9 to 10 mm, and another angle indicatormay be used for the range 10 to 11 mm. These values are merelyexemplary, and any suitable ranges may be used.

Note that because the angle may be measured from roughly the center ofthe pupil, there is little distortion of the angle caused by the cornea.If the cornea imparts a magnification an image of the segments formingthe angle, the segments themselves may appear to grow or shrink in size,but the angle between the segments remains essentially unchanged. Thisholds for a wide range of cornea radii, and a wide range ofmagnifications caused by the cornea.

It is instructive to perform some trigonometry to more accurately showthe graphical dependence of measured angle A and capsular bag diameterdynamic range. Similarly, for relatively long straight segments (highq), there is low sensitivity and high dynamic range.

In some embodiments, it is preferable if the vertex, or intersectionbetween the straight segments, is located at or near the center of thering for at least part of the range of use. The circles superimposed onthe various plotted curves in FIG. 5 show the operating condition atwhich the vertex is at the center of the ring. Note that for shortsegments (q<0.5), there is no condition under which the vertex can belocated in the center of the ring; these segments are just too short toextend to the center, regardless of angle A.

Note that for q=0.6 (i.e., where the straight segments are 20% longerthan the radius of the “closed” ring), the vertex falls at the center ofthe ring at a measured angle A of 60 degrees. In one embodiment, thismay be a preferable set of conditions; the plotted region for q=0.6 isenlarged and is shown in FIG. 6.

For FIG. 6, we choose a convenient set of numbers, which are merelyexemplary and are not intended to be limiting in any way. For instance,if we wish to measure capsular bags having a diameter in the range of 11mm to 13 mm, we use an angle indicator having a “closed” diameter of 10mm and a short segment length of 6 mm, and detect angles between 30 and90 degrees. If our detection scheme allows us to detect angle A to thenearest 15 degrees, we may measure the diameter of the capsular bag tothe nearest 0.5 mm (based on the 10 mm diameter of the angle indicator).These values are merely exemplary, and any lengths and diameters may bescaled upwards or downwards. Other suitable values may also be used.

Note also that the mathematical analysis that generates the plots ofFIGS. 5 and 6 is approximate, and assumes that the lengths of thering-shaped segments and the two straight segments all remain constantthroughout operation. This is only an approximation, and one of ordinaryskill in the art will readily appreciate that more sophisticatedsimulations may be performed that account for local stresses anddeformations, bending of the materials, and other effects not consideredin the simplistic analysis presented above. D, which is not truly linearas shown schematically in FIG. 2, but has a more complicated dependence.

FIG. 4 shows an exemplary geometry for one embodiment of an angleindicator. We assume for this simplistic analysis that the lengths ofthe incomplete annulus (i.e., the open ring-shaped segment) and thestraight segments remain constant during use; this is a goodapproximation for this purpose.

Both the length of the incomplete annulus and the length of eachstraight segment may be related to a “closed diameter” D₀, which is thediameter of the angle indicator when the segments are parallel, or“closed”. The length of the incomplete annulus is πD₀, and the length ofeach straight segment is qD₀, where q is a dimensionless quantity thancan between 0 and 1. When q is 0.5, the straight segments extend toexactly the center of the ring when the ring is “closed”. When q is 1,the straight segments extend all the way to the opposite end of the ringwhen the ring is “closed”. When q is 0, the straight segments areinfinitesimally small.

During use, the angle indicator expands to a diameter of D, with ameasured angle A between the straight segments. Length y and angle a aremathematical constructs. We attempt to solve for A in terms of D.

First, solve for y: y=D sin(a/2).

Next, we express angle a in terms of the length πD₀ of the incompleteannulus: a=(2π−2πD₀/D).

Plug into expression for y: y=D sin(π−πD₀/D)=D sin(πD₀/D)

Can also solve for y in terms of a and qD₀: y=2 qD₀ sin(A/2)

Set these two expressions for y equal to each other and rearrange toget: sin (A/2)=sin(πD₀/D)/(2 qD₀/D)

Solve for A and rewrite as A=2 sin⁻¹([π/2q] [ sin(πD₀/D)/(πD₀/D)])

FIG. 5 is a graph of the above equation, which predicts capsular bagdiameter D versus measured angle A, for several values of q.

The choice of q is related to both sensitivity and dynamic range. Forrelatively short straight segments (low q), there is high sensitivityand low

The discussion thus far has focused primarily on the angle indicator,which generates an angle as a function of the capsular bag size. Thefollowing paragraphs focus primarily on an exemplary protractor forreading the angle generated by the angle indicator.

Once the angle indicator is inserted into the capsular bag and expandedto its fullest extent, the straight segments form an angle that isvisible through the cornea. The angle may be viewed by eye, or may beviewed through a microscope, camera, or any suitable imaging system.Because the angle may be subject to distortion by a camera or imagingsystem, one angle measurement embodiment is a protractor that may beremovably placed on the cornea.

For the purposes of this document, the term “protractor” may include anyinstrument or device that can read an angle visually or by electronicmeans. For instance, a protractor may include a flexible sheet (e.g., acontact lens) having radial marks, a circular device having regularmarkings at predetermined locations along its circumference, and soforth. A protractor may also include software that can return a measuredangle value for an angle embedded within an image. Additionally, aprotractor may include a calibrated reticle for an optical instrument,such as a microscope or a camera. The increments on the protractor mayinclude one degree, five degrees, 10 degrees, 15 degrees, 20 degrees, 25degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, or any suitableincrement. Alternatively, the protractor may be marked with indicia thatcorrespond directly to the capsular bag size or appropriate rangescorresponding to available implant sizes.

An exemplary protractor 70 is shown in the isometric drawing of FIG. 7and the three views of the plan drawing of FIG. 8.

The protractor 70 has a generally circular ring 71 that is sized to reston the cornea to allow measurement of the angle from the angleindicator. The ring 71 is small enough to fit on the eye of the patient,and large enough to surround the pupil of the eye. A typical range ofdiameters for the protractor ring may be from about 3 mm to about 12 mm,or from about 5 mm to about 8 mm.

Note that the straight segments 32 and 33 of the angle indicator 30 areviewable from roughly the center of the pupil, rather than requiring ameasurement taken at the edge of the capsular bag. As a result, ring 71of the protractor need not extend all the way to the edge of thecapsular bag or to the edge of the cornea. The ring 71 may optionallyhave rounded or chamfered edges that may reduce the risk of scratchingthe cornea.

The protractor 70 has a reference portion 72 that has radial edges 73and 77. During use, the reference portion 72 generally extends out ofthe plane of the ring 71, so that it may rest upon or extend over thecornea, which is curved. When viewed from the front, the intersection ofradial edges 73 and 77 may fall at or near the center of the ring 71,and/or at the intersection of the straight segments 32 and 33 (e.g., atthe hinge 39). Note that the reference portion 72 may deform so thatthis intersection of radial edges 73 and 77 may lie away from the centerwhen the protractor is not in use.

In one embodiment, the protractor is rigid, so that the protractorroughly maintains its shape before, during and after use. In thisembodiment, the reference portion 72 may extend out of the plane of thering 71 in its relaxed state before use. Alternatively, the referenceportion may 72 may be located roughly in the plane of the ring 71 beforeuse, and may pivot in the anterior direction during use. The pivotingmay occur around a weakened portion of the reference portion, which mayinclude an optional hole or void area 81. In some embodiments, the voidarea 81 may have a more complex shape that the hole shown in FIG. 7, forexample, to provided a weakened zone with predetermined bendingcharacteristics or to avoid confusion that the void area 81 representsan alignment mark with the straight segments 32 and 33.

In another embodiment, the protractor 70 is flexible, and may be drapedonto the cornea of the eye. Such a flexible protractor conformsgenerally to the shape of the cornea, without significantly deforming inthe plane of the protractor. The protractor 70 may be made from alargely transparent material, and may include markings or features thatindicate predetermined angle values. For instance, the protractor 70 mayinclude a central feature that may be overlaid with the hinge 39 duringuse, and various angular features, such as reticle marks or other radiallines or features. In one embodiment of a flexible protractor 70, theprotractor may be formed on or be made integral with a contact lens thatis placed onto the cornea during use.

For the protractor 70 of FIG. 7, the protractor is positioned during useso that one of the radial edges 73 and 77 lines up with one of thestraight segments 32 and 33. The other straight segment falls elsewherearound the circumference of the ring, and may fall near one of severalcalibration features, such as notches, tabs, holes, extensions,annotations, colors or members.

For instance, if radial edge 73 is aligned with straight segment 32,then straight segment 33 may fall near one of feature 74, feature 75 orfeature 76. The features may be in calibrated increments, such as 30degrees, 20 degrees, 15 degrees, 10 degrees, or any suitable increment.For instance, if the increment is 30 degrees between each of thefeatures 74-76, then if the straight segment 32 falls closest to thefeature 74, then the angle of the indicator is closest to 30 degrees.Similarly, if the straight segment 32 falls closest to the feature 76,then the angle of the indicator is closest to 90 degrees.

In addition, there is a second set of radial edge 77 and features 78-80,which may be used equally as well as the first set of radial edge 73 andfeatures 74-76. The second set may be calibrated with the same angularincrement as the first, or with a different angular increment as thefirst.

Alternatively, there may be more than three or fewer than threefeatures. In addition, the features may be evenly or unevenly spaced.

Once the measurement has been taken, the protractor 70 may be removedfrom the cornea of the patient. In one embodiment, the protractor 70 maybe removed by grasping it with the hole 81, or by an optional elevatedfeature or tab (not shown).

There may be other suitable angular measurement devices that may beused, as alternatives to the device shown in FIGS. 7 and 8. Forinstance, a more conventional protractor may be used, with notches, tickmarks, lines, or other visual cues extending around the circumference ata prescribed interval, such as every 30 degrees, or any other suitableinterval. This more conventional protractor may lack the referenceportion 72. As another example, the protractor may be made from a softmaterial that is draped over the cornea or rests on the facial tissuethat surrounds the eye, rather than on the eye itself. Alternatively,the angle may be measured from an image formed of the eye on a screen orin software. As a further alternative, there may be an angular reticlesupplied with a camera or microscope, which may allow a reading of theangle.

The angle indicator 30 may be made integrally as a single unit, or maybe made from several pieces that are assembled. The assembled pieces maybe made from the same or from different materials.

Both the angle indicator 30 and the protractor 70 may be made from anysuitable biocompatible and flexible materials. For instance, either orboth may be made from silicone or any polymeric material, PMMA, or anyother suitable material. In one embodiment, the material or materialsused may be moldable, and may not be hydrophilic. In one embodiment, thematerial is sterilizable by autoclave, by ETO, or by any suitablesterilization process. The angle indicator 30 and protractor 70 may bemade from the same or from different materials. The angle indicator 30and protractor 70 may be made of a tinted, opaque or fluorescingmaterial, so that they may easily be read visually.

In one embodiment, the angle indicator and protractor may be supplied inpre-sterilized, sealed packages that accompany an intraocular lens. Boththe angle indicator and protractor may be unsealed when needed, anddisposed of once a measurement has been taken.

In one embodiment, there may be sets of angle indicators andprotractors, with each set corresponding to a different range ofcapsular bag sizes. For instance, one set may be used for a size rangeof 9 to 10 mm, and another set may be used for a size range of 10 to 11mm. Each set may be color-coded so that the particular protractor iseasily associated with its corresponding angle indicator, and themeasured angles are easily associated with their proper measuredcapsular bag sizes. Alternatively, there may be other identifyingcharacteristics for matched sets of angle indicators and protractors,such as texture, etching, surface characteristics, ridges and so forth.

In one embodiment, the outer edges of the angle indicator may expandthrough viscoelastic/OVD in the capsular bag.

In one embodiment, the straight segments, or central arms, of the angleindicator may extend past the center of the angle indicator. Theselonger straight segments may fill a larger area of the pupil, and mayprovide an easier measurement than smaller or shorter straight segments.

In one embodiment, the angle indicator may be inserted into the capsularbag by an injector.

In one embodiment, the angle indicator may include a tether, so that theangle indicator may be more easily withdrawn after the measurement hasbeen taken. The withdrawing may be done directly by the tether.Alternatively, the tether may attach the angle indicator to an injector,so that the withdrawal may be done by the via injector.

In one embodiment, the angle indicator may include one or more loops onthe straight segments or on the incomplete annulus that extend in theanterior direction (i.e., away from the patient's eye), for positioningand removal of the angle indicator.

In one embodiment, the angle indicator may include a tether, so that theangle indicator may be more easily withdrawn after the measurement hasbeen taken. The withdrawing may be done directly by the tether.Alternatively, the tether may attach the angle indicator to an injector,so that the withdrawal may be done via the injector.

In one embodiment, the modulus of the angle indicator material and thewidth of the various angle indicator sections may be varied, so thatreliable measurements may be made without excessively stretching thecapsular bag.

In one embodiment, the angle indicators are provided in a kit, with eachangle indicator having a different expansile strength. Such a kit may beused to determine the elasticity of a particular evacuated capsular bag,in order to best determine the most compatible accommodating intraocularlens.

In one embodiment, the angle indicators are provided in a kit, with eachangle indicator having a different axial thickness. Such a kit may helpmatch the measurement of the capsular bag size to the axial thickness ofthe intended implanted intraocular lens, both at the edge of the lensand centrally.

In one embodiment, the central linear arms, or straight segments,include overlapping, curved vernier extensions. With reference to theexemplary design of FIG. 3, straight segment 32 may include one or moretangentially-curved extensions that protrudes toward segment 33, andstraight segment 33 may also include one or more tangentially-curvedextensions that protrudes toward segment 32, with thetangentially-curved extensions being located next to each other. In thismanner, the angle may be read directly from the extensions, rather thanwith an additional external device such as a protractor.

In one embodiment, the incomplete annulus 31 may include extensions ortabs protruding from one or both of the straight segments 32, 33 anddisposed along the circumference of, and in the plane of, the incompleteannulus 31. These optional extensions may help maintain the capsularcircularity in the region between the straight segments 32, 33.

In addition to measuring the capsular bag size for intraocular lensimplantation, the angle indicator, or variations thereof, may be usedfor other fields as well, such as measuring the diameters and stenosisof body cavities, especially in endoscopic and catheter-based proceduresfor sizing shunts and implants. The angle indicator allows estimation ofa particular diameter, regardless of viewing magnification. This mayalso be used in the fields of interventional cardiology, as well asvascular, bariatric and gastroenteric surgeries. Furthermore, the angleindicator, or variations thereof, may also be used to measure the sizeof the anterior chamber or other cavities of the eye.

The description of the invention and its applications as set forthherein is illustrative and is not intended to limit the scope of theinvention. Variations and modifications of the embodiments disclosedherein are possible, and practical alternatives to and equivalents ofthe various elements of the embodiments would be understood to those ofordinary skill in the art upon study of this patent document. These andother variations and modifications of the embodiments disclosed hereinmay be made without departing from the scope and spirit of theinvention.

1. A method for measuring the size of a capsular bag of an eye,comprising: inserting an angle indicator into the capsular bag, theangle indicator comprising: an incomplete annulus and a pair of joinedarms disposed within the incomplete annulus, the joined arms operablycoupled to first and second ends of the angle indicator; reading anangle from the angle indicator; removing the angle indicator from thecapsular bag; and converting the angle to a capsular bag size.
 2. Themethod of claim 1, further comprising positioning the angle indicatorsuch that the joined arms are at least partially visible through thepupil.
 3. The method of claim 1, wherein reading comprises: forming aphysical angle between two segments of the angle indicator;superimposing a protractor onto the physical angle; comparing thephysical angle to at least one calibration feature on the protractor;and identifying the angle from the at least one calibration feature. 4.The method of claim 1, wherein converting comprises: identifying apredetermined relationship between the angle and the capsular bag sizedescribed by at least one of a formula, a table, and a graph; and usingthe predetermined relationship to estimate the capsular bag size.
 5. Themethod of claim 1, further comprising reading the angle from a centralportion of the angle indicator.
 6. The method of claim 1, furthercomprising expanding the angle indicator to coincide with an equator ofthe capsular bag.
 7. An angle indicator for measuring the size of acapsular bag of an eye, comprising: a compressible, incomplete annulushaving a first end, a second end, an interior and an outer surface thatremains essentially circular when the incomplete annulus is compressed,the outer surface having a diameter that varies in response tocompression of the incomplete annulus; a first segment attached to thefirst end of the incomplete annulus and extending into the interior ofthe incomplete annulus; and a second segment attached to both the secondend of the incomplete annulus and a distal end of the first segment;wherein the first and second segments form an angle, the angle beingindicative of the diameter of the outer surface of the incompleteannulus.
 8. The angle indicator of claim 7, wherein the first and secondsegments are configured to form an angle visible through the pupil of aneye when the angle indicator is disposed in the capsular bag of the eye.9. The angle indicator of claim 7, wherein the first segment is hingedlyattached to the first end of the incomplete annulus; and wherein thesecond segment is hingedly attached to both the second end of theincomplete annulus and the first segment.
 10. The angle indicator ofclaim 7, wherein the first segment comprises a first straight portion,and wherein the second segment comprises a second straight portion. 11.The angle indicator of claim 7, wherein the incomplete annulus has avarying radial thickness along its length, the radial thickness beinggreater at the midpoint between the first and second ends than at boththe first and second ends.
 12. The angle indicator of claim 7, whereinthe angle formed by the first and second segments is acute.
 13. Theangle indicator of claim 7, wherein the incomplete annulus and the firstand second segments are formed integrally.
 14. The angle indicator ofclaim 7, wherein the incomplete annulus and the first and secondsegments are joined by hinges, each hinge comprising a reduction inin-plane thickness.
 15. The angle indicator of claim 7, wherein thefirst and second segments have lengths greater than half the diameter ofthe incomplete annulus and less than the diameter of the incompleteannulus.
 16. The angle indicator of claim 7, wherein the first andsecond segments have lengths equal to each other.
 17. The angleindicator of claim 7, wherein the incomplete annulus and the first andsecond segments have rounded edges.
 18. An apparatus for measuring thesize of a capsular bag of an eye, comprising: an angle indicatorcomprising an incomplete annulus and a pair of arms joined at anintersection therebetween, the arms disposed within the incompleteannulus, the joined arms operably coupled to first and second ends ofthe angle indicator and configured so that an angle formed by the armsvaries in response to a diameter of a capsular bag of an eye; and aprotractor disposed in front of the angle indicator for measuring theangle formed by the arms, the protractor comprising: an alignment markdisposed in front of an intersection of the arms of the angle indicatorand at least one radial reference edge disposed along one of the arms;and a plurality of arcuately disposed features located at predeterminedangular locations from the at least one radial reference edge.
 19. Theapparatus of claim 18, wherein each of the arms of the angle indicatorcomprises a straight portion.
 20. The apparatus of claim 18, wherein thefeatures of the protractor are at least one of protrusions, notches, andholes.
 21. The apparatus of claim 18, wherein the features of theprotractor are at least one of a color-code and an alphanumeric symbol.22. The apparatus of claim 18, wherein the predetermined angularlocations of the protractor are evenly spaced.
 23. The apparatus ofclaim 18, wherein the protractor is flexible and is configured to bedraped over a cornea of the eye.
 24. The apparatus of claim 18, whereinthe protractor further comprises an annular portion and a referenceportion disposed in an interior of the annular portion, the referenceportion including the radial reference edge, the features disposed alongthe annular portion.
 25. The apparatus of claim 24, wherein theintersection of the arms of the angle indicator is visibly centered inthe annular portion.
 26. The apparatus of claim 24, wherein thereference portion extends anteriorly away from the annular portion. 27.The apparatus of claim 24, wherein the annular portion has a diameterless than the diameter of a cornea of the eye.